Calcareous nannofossil abundances in Mesozoic sediments of ODP Leg 129 holes

Calcareous nannofossils were studied from Jurassic and Cretaceous sediments drilled in the western Pacific during Ocean Drilling Program Leg 129. Mesozoic sediments at Sites 800, 801, and 802 are dominated by volcaniclastic turbidites, claystones, porcellanites, and radiolarites. Pelagic limestones are limited to the middle Cretaceous, and a few calcareous claystones were recovered in the Upper Jurassic section at Site 801. We documented the distribution of nannofossils, their total abundance, preservation, and relative species abundance based on semiquantitative and qualitative studies. Preservation of the calcareous nannofloras is poor to moderate, and the total abundance fluctuates from rare to very abundant. Marker species proposed for the middle and Late Cretaceous were recognized, allowing the application of standard nannofossil biozonations. At Site 800 calcareous nannofloras are abundant and moderately preserved in the Aptian-Cenomanian, and nannofossil biostratigraphy constitutes the basic stratigraphic framework for this interval. Radiolarians are the most abundant and persistent group throughout the sequence drilled at Site 801. Long intervals are barren of nannofloras and assemblages are usually characterized by low abundance and poor preservation. Nannofossil biostratigraphy was applied to the upper Aptian-Cenomanian interval and a few marker species were recognized for the late Tithonian. At Site 802 Cretaceous biostratigraphy is mainly based on calcareous nannofossil biozones corroborated by radiolarian and palynomorph events in the late Aptian-Coniacian age interval. A hiatus was indicated between the Santonian and the late Campanian, and another is suspected in the interval between the Cenomanian and the Coniacian.

Distribution and abundance of nannofossils in DSDP Site 89-585

Late Aptian through middle Eocene nannofossil assemblages were recovered from a continuously cored section at Site 585. Poorly preserved assemblages of low diversity were observed in samples taken throughout both upper Aptian and/or lower Albian sandstone and mudstone and middle Cenomanian to lower Turonian claystone at the base of this section. A 70-m interval barren of nannofossils separates these poorly preserved assemblages from those recovered from an upper Campanian chalk farther uphole. This chalk marks the most significant change in carbonate deposition at this site, and deposition of interbedded zeolitic claystone and sediment of varied nannofossil content proceeded without major interruption until the early Paleocene (Fasciculithus tympaniformis Zone, CP4). A middle Eocene chalk (dated by nannofossils) unconformably overlies lower Paleocene sediment in both Holes 585 and 585A. Only a few interbeds of zeolitic claystone are present within 100 m of nannofossil-rich sediment above this unconformity. This entire interval is cautiously assigned to the Discoaster sublodoensis Zone (CP 12), which indicates a sedimentation rate almost an order of magnitude higher than expected from normal pelagic sedimentation. The most obvious feature of the assemblages examined from these cores is the amount of reworked material. Rare Nannoconus elongatus and Braarudosphaera sp. in several upper Campanian to middle Eocene samples demonstrate the contribution of pelagic material from upslope and, along with other reworked species throughout the Upper Cretaceous samples examined, provide evidence contradictory to an excursion of the calcium compensation depth to deep basinal settings in the western Pacific during the Campanian-Maestrichtian time (Thierstein, 1979). The overwhelming dominance of reworked species in all middle Eocene samples examined and the persistence of these assemblages throughout such a large thickness of sediment suggest that currents that redeposited material intensified at this time and may be associated with the formation of the lower Paleocene/middle Eocene unconformity at this site. A single surface core of calcareous ooze taken from Hole 585A dated as early Pleistocene contains abundant and well-preserved late Miocene and Pliocene species.

Calcareous nannofossils of ODP Sites 149-897 and 149-901

Mesozoic calcareous nannofossil assemblages recovered during Ocean Drilling Program Leg 149 from the Iberia Abyssal Plain off the coast of Portugal were examined to determine the age of the rifting processes that affected the western Iberia Margin. Dark carbonaceous claystones (black shales) recovered from Site 901 contain highly diverse and abundant Tithonian calcareous nannofossil assemblages. Careful examination and documentation of this material has extended the ranges of numerous Jurassic and Cretaceous species and detailed a significant Late Jurassic assemblage turnover observed in the calcareous nannofossil record. The Lower Cretaceous sequence consists of intervals of serpentinized peridotite intercalated between various breccias and dark claystones. With the exception of a few samples, calcareous nannofossils are few and moderately preserved. The age of nannofossils within these varied sedimentary lithologies ranges from the late Barremian to the late Aptian. Eight new species are described: Ansulasphaera covingtonii, Clepsilithus meniscus, Conusphaera sinespina, Crepidolithus parvulus, Diazomatholithus galicianus, Percivalia arata, Rotelapillus pleoseptatus, and Tranolithus incus. Also proposed are five new combinations.

Early Cretaceous spores and pollen of ODP Leg 103 holes

About 80 species of spores and pollen grains were recorded during detailed palynological investigations of selected Lower Cretaceous sections from Holes 638B and 638C and the bottom of Hole 641C. Most of them are long-ranging taxa with worldwide distribution. However, on the Iberian margin and in the southern European basins, Trilobosporites canadensis, Trilobosporites bernissartensis, Parvisaccites amplus, Foveosporites subtriangularis, and Ephedripites multicostatus seem to be index species of the Valanginian to late Aptian interval. Clavatipollenites was not recovered in the Barremian marginal marine sediments.

Cretaceous dinoflagellate cysts of ODP Leg 103 holes

The dinoflagellate cyst assemblages in 42 samples collected from Sites 638 and 639 were analyzed. All samples from Site 639 are barren; relatively poor assemblages occur in samples from Site 638. The distribution of 61 dinoflagellate cyst taxa identified in samples from Holes 638B and 638C are tabulated. The assemblages from Site 638 are comparable to those of Tethyian stratotypes and from neighboring areas, which permits age determinations and correlations between Holes 638B and 638C. The interval from Cores 103-638C-14R to 103-638C-1R is late Berriasian through Valanginian in age. In Hole 638B, the interval from Core 103-638B-43R to Section 103-638B-23R-2 is dated as early Valanginian through middle Barremian. Sections 103-638B-21R-2 and 103-638B-21R-1 are late Aptian in age. Taxonomic remarks are made about some species; a new dinoflagellate cyst Heterosphaeridiuml galiciae is described.

(Figure 2) Organic carbon content, stable isotope ratios, TEX86 index and sea surface temperature reconstruction for the early Aptian of ODP Hole 198-1207B

The Cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric CO2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events (OAEs). Yet, the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained. Here we present a high-resolution record of sea-surface temperatures (SSTs) reconstructed using the TEX86 paleothermometer for a sequence of early Aptian organic-rich sediments deposited during the first Cretaceous OAE (OAE1a) at Shatsky Rise in the tropical Pacific. SSTs range from ~30 to ~36 °C and include two prominent cooling episodes of ~4 °C. The cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter. SST instability recorded during the early Aptian in the Pacific is comparable to that reported for the late Albian-early Cenomanian in the Atlantic, suggesting that such climate perturbations may have recurred during the Cretaceous with concomitant consequences for biota and the marine environment.

Barremian-Aptian dinoflagellate cyst assemblages

Quantified organic-walled dinoflagellate cyst (dinocyst) assemblages are presented for two sedimentary successions deposited in neritic environments of the Tethys Ocean during the Barremian and Aptian in an attempt to reconcile established dinocyst biostratigraphic schemes for Tethyan and Austral regions. One section is at Angles, southeast France (the Barremian stratotype section); the other is at Deep Sea Drilling Project Site 263, off northwest Australia. We also construct a carbon isotope record for Site 263 using bulk organic carbon. Both sections contain abundant, well-preserved dinocyst assemblages. These are diverse, with 89 taxa identified at Angles and 103 taxa identified at Site 263. Of these, more than 93% are cosmopolitan. When combined with other work at Angles and Site 263, we found that nine dinocysts have their first occurrence (FO) or last occurrence (LO) at both locations. These dinocyst events are, in alphabetical order: LO of Cassiculosphaeridia magna, FO of Criboperidinium? tenuiceras, LO of Kleithriasphaeridium fasciatum, LO of Muderongia staurota, FO of Odontochitina operculata, LO of Phoberocysta neocomica, FO of Prolixosphaeridium parvispinum, FO of Pseudoceratium retusum var. securigerum, and FO of Tehamadinium sousense. Although these events support a Barremian-Aptian age for both sections, their stratigraphic order is not the same in the sections. The d13Corg record at Site 263 displays a characteristic series of changes that have also been recorded in other carbon isotope curves spanning the Late Barremian-Early Aptian. Such independent dating (along with ammonite zones at Angles) suggests that three of the nine dinocyst events are approximately isochronous at Angles and Site 263: the LO of K. fasciatum in the mid Barremian, the FO of P. retusum var. securigerum and the FO of C.? tenuiceras in the earliest Aptian; the other six dinocyst events are diachronous. Dinocyst assemblages at Site 263 can be loosely placed within existing Australian zonation schemes, providing much-needed calibration. Our data suggest that the Muderongia testudinaria Zone ends in sediments of mid Barremian age, the succeeding Muderongia australis Zone extends into the Early Aptian, and the younger Odontochitina operculata Zone begins in Early Aptian deposits. The boundary between the M. australis and O. operculata zones, and the Ovoidinium cinctum (as Ascodinium) Subzone, positioned at the top of the M. australis Zone when present, could not be recognized incontrovertibly. Interestingly, however, this horizon broadly correlates with the onset and extent of the Selli Event, a time of major biogeochemical change.